Radiation detectors



Oct. 16, 1956 E. H. wooDHULL RADIATION DETECTORS Filed Jan. 30. 1953 2Sheets-Sheet' 1 Oct. 16, 1956 E- H- WOODHUl-l- 2,767,321

RADIATION DETECTORS Filed Jan. 50, 1953 2 Sheets-Sheet 2 @if y @my W W f@www fr. M MMM ATTORNEY5 United States Patent RADIATION DETECTORS ElliotH. Woodhull, Norwalk, Conn., assiguor to The Perkin-Elmer Corporation,Norwalk, Conn., a corporation of New York Application January 30, 1953,Serial No. 334,144

18 Claims. (Cl. 250.-43.5)

This invention relates to detectors for radiant energy, and is concernedmore particularly with a novel device for detecting and measuringinfrared radiation. The new detector is of the type, in which theradiation falling upon the device is measured by the changes in capacityof an electrical condenser having a movable plate in the form of amembrane, which is deected by a gas heated and expanded by theradiation. Detectors of the gas-operated condenser type are not new andare disclosed in prior patents, of which those to Hays 1,954,204, April10, 1934, and Hall 2,115,578, April 26, 1938, are typical. The detectorof the invention difers from and is superior to those of the patentsmentioned in that it is not affected by translational accelerations andis thus not subject to errors arising therefrom. The desired results areobtained in the detector without loss of sensitivity or complicatedstructure and the detector is relatively simple to construct and adjustfor operation.

The detector of the invention comprises a central chamber and a pair ofouter chambers lying on opposite sides of the central chamber andseparated therefrom by respective electrically conductive membranes. Themembranes lie with their planes parallel, and within each outer chamberis a fixed plate lying in juxtaposition to the membrane and cooperatingwith the latter to form an electrical condenser. The three chambers allhave a filling of the same gas or gas mixture at the same pressure and,in one form of the detector, the outer chambers are isolated from eachother and the centers of gravity of the gas masses therein are equallyspaced from the center of gravity of the gas mass in the central chamberand the three centers of gravity lie on a line normal to the planes ofthe membranes. In an alternative form, the ydetector is constructed withthe outer chambers so connected that the combined gas masses therein actas one. In this form, the center of gravity of the combined gas massesis coincident with that of the gas mass in the central chamber. In bothforms of the detector, translational accelerations tendingl to move themembranes relative to their fixed plates cause an increaseV in thecapacity o f one condenser, which is balanced by a decrease in'Vcapacity in the other. The condensers are connected in parallel and theaccelerations, accordingly, produce no net capacity change in thecircuit containing the condensers and no detector signal.

For a better understanding of ther invention, reference may be made tothe accompanying drawings, in which Eig, 1- is a horizontal sectionalview throughV Vone form of the new detector;

Fig. 2 is a fragmentary sectional view on the same line as Fig. 1, buton an enlarged scale;

IFig. 3 is a sectional view on. the line 3-3 of Fig. l;

Fig. 4 is a sectional view on the line 4-4 of Eig?. 3;

Fig'. 5 is a fragmentary sectional view on. the saine line Fig. 3v andshowing the' use of an adjusting device;

2,757,321 ateted Oct. 16, 1956 gig. 6 is a sectional view on the line 66 of Fig. l; an

Fig. 7 is a schematic view including a wiring diagram.

The detector of the invention is illustrated in the drawings in use in anon-dispersion analyzer of the type disclosed in the applications ofWoodhull and Tisdale, Ser. No. 321,662, tiled November 20, 1952, whichmatured as U. S. Patent No. 2,688,090, and Woodhull, Borden, andMontpas, Ser. No. 334,143, tiled January 30, 1953, for both of whichapplications I am one of the co-applicants. The analyzer referred tocomprises a housing 10 formed to provide passage 11, 12, and 13 forbeams of radiation from a source, and the beams of radiation are choppedin such manner that radiation in two beams falls upon the detector atthe same time and in alternation with radiation in the third beam. Thepassages in the housing may be used as a lter cell and the filter gasmay be admitted into the passages in the housing through a connection 14having a Valve 15.

The detector comprises a housing generally designated 16 and preferablymade of a block of metal 17, which is formed with a central chamber 18and outer chambers 19, 20 on opposite sides thereof.v The chambers maybe formed by drilling, in which event they are of circular crosssection, as shown. The chamber 18 has an open end aligned with the endsof the passages in housing 10 and closed by a window 21 of infraredtransmitting material, such as a suitable crystal.

The housing 16 is secured to housing 1t) in any suitable Way, as byscrews passing through openings in block 17 and into the end of housingV10. The end wall of block 17 opposed to the outer face of housing 1i) isformed with a channel encircling the Window and containing a gasket 22of a suitable packing material. The end wall of housing 10 is alsoprovided with a channel encircling the opening in the housing leading towindow 21 and a packing 23 in the form of an O-ring is mounted in thechannel in position to engage the outer face of the window. The packingmaterial used for the gasket and ring and elsewhere in the detector maybe the tetrauoroethylene polymer sold commercially under the name Teon.

The outer ends of chambers 19 and 20 are. closed by plates 24, 2S, whichare held in place by screws 26 pass.- ing through the plates andthreaded into block 17. Gaskets 27, 2,8 of suitable packing material areseated in channels in the ends of the block in position to be engaged byplates 24, 2,5 and serve to prevent leakage from the chambers.

lCC

The chambers; 18, 19, and 20 are connected by aV passage 29 in the outerwall of block 17 and the passage is provided with a conical seat 30opening through the outer face of block 17 and engageable by the plug31jA ofV a valve. 'Ille plug lies mainly within a housing 32 secured to;the o nter face of block 17- and is movable toward and away fromv itsseat by an adjustment screw 33 extending-through an opening in the outerwallV of housing 32 and provided at its exposed end with a disc 34, bywhich the screw may be turned-. In order to` prevent leakagel betweenpassagev 29- and the atmosphere, whenV plu-g 31 is unseated, ,the outerend of the plug is provided with a dans@ 35;, t0 which' is. Secured Queand of ametalbellows- 36, the other end of thel bellows being secured totheV wall of block 17 around the conical, seat 30.` The outer wallofblock 17 isV provided with a passage 37 (Big. 6) leading to. theinterior ofthe valve seat:l 30, and the passage is provided with aconnection 38 containing avalve 39.` By rotation of the screw 33, theplugr may be backed out, so that. the three chambers 1:8, 19, and 2Qyare connected by passage 29 and can be evacuated through connection 38.Thereafter, in preparing the detector for use, the av gas or gas mixtureto the desired pressure and'the chambers are then shut off from oneanother by seating the p1ug'31; For someV purposes, it may be desirableto provide a connection between the chambers 19, 20 in the form of anopen passage 40 (Fig. 6), which is of such cross-sectional area that thegas masses in the two chambers act as a single mass. Instead of a singlepassage, the connection between the chambers may be made by two openpassages similar to passage 40 with the passages connecting the chambersat opposite sides of their axes. Thus, one passage may connect thechambers at their tops and the other at their bottoms.

p Each 'of the chambers 19, `20 contains Aa variable condenser, thecapacity of which varies with changes in pressurev within the centralchamber 18 and, as the two condensers are alike, only that in chamber 19need be described. Such a condenser comprises va plate 41 (Figs.`

1, 2) mounted on the inner wall of chamber 19 and provided with acentral cavity 42 facing that wall, the cavity Vbeing encircled by achannel 43 containing an O-ring 49 of capillary size, which lead fromthe cavity 47 to theV interior of chamber 19 at the periphery of plate41.

The flange 48 is provided with a circumferential rib 50 on its outerface and the peripheral margin of a thin flexible metallic diaphragm 51overlies the outer face of the flange and is clamped against that faceby a flat ring 52 having a face of the same dimensions as flange 48 andprovided with a'circumferential channel, into which the diaphragm isforced by rib G. The plate 41 and ring 52 are secured in position byscrews 53 passing through the ring, the membrance, and the plate andentering the block 17. The clamping of the margin of the diaphragm beris provided with-a central boss 59 extending fromA its outer face andinternally threaded, and with a'cylindrical ange 60 lying concentricwith the boss 59 and extending from the inner face of the member. Acircular Vplate 61 rests on the inner face of the flange 60 and the vplate has a peripheral flange 62 overlapping ange 60 and a central boss63 aligned with boss 59. An outer adjustment screw 64 with an internallythreaded bore through it is screwed into boss 59 and an inner adjustmentscrew 65 is screwed into the bore through screw 64 and has its endsecured in a socket in boss 63 on plate 61. Screw 64 has a non-circularhead 66 and the internal and external threads on the two screws are of'l diierent pitch.

The membrane 51 forms the movable plate of* a condenser, ofwhich plate61 forms the fixed plate, and. the initial capacity of the condenser isadjustable byro" tating screw 64. As the screw is thus moved inone'direction or another, the central part of plate 61 withinflange 60on plate 57 is moved toward and away from the membrane, while its marginis held in iixed position by engagement with flange 60. Under vnormalconditions, plate 61 is Vdistorted by having its central portion bulgedoutwardly to a greater or less extent, and this causes a force to beexerted on the threads of screws 64 and 65 tending to lock the screws inadjusted position.

The usev of the Vtwo sets of threads on screw 64 provides" chambers arefilled with I a Vernier adjustment, so that the position of the centralpart fvplate 61 relative to the membrane can be Vadjusted within verysmall limits.

In the use of the new detector in the instruments of the co-pendingapplications, above identied, for the determination of the amount of agas'of interest present in a sample to be examined, the chambers 18, 19,and 20 are evacuated through the connection 38 and are then iilled gasto produce optimum response.

with the gas of the interest at the desired pressure giving maximumdetector sensitivity. Asv is well known in the- .are connected to thecentral chamber 18' through the O-ring 70 of packing material.

capillaries 49 and the openings 45 and 46. v Thereafter, the capacitiesof the condensers are balanced by adjustment of the capacity of onecondenser by varying the spacing between its forced plate 61 and itsmembrane 51..

The ,adjustment of the capacity of either or both condensers should bemade while the chambers 18, 19,

and 20 are filled with the gas of interest at the pressure to be used inthe operation of the instrument. Accordingly, for the purpose of makingthe adjustment, the plates 24, 25, which close the chambers 19 and 20are removed and replaced by plates 67. Each plate 6,7 is

provided with a central boss 68 having an opening for the stem of an endwrench 69, the opening being formed with an internal circumferentialchannel containing an The Vwrench has a socket which ts over the head 66on yscrew 59, and the outer end of the stem is provided with a knurledhead "71, by which the stem may be rotated to turn screw 66. lnadjusting the capacity or the condensers after the wrench plates 67 havebeen mounted in position, the three chambers 18, 19, and 20 are filledwith the gas at the proper pressure and plug 31 is seated. Thereafter,the detector is vplaced upon a shake table, which subjects it torepeated translational acceleration. detector is being shaken, anyfurther adjustment of the fixed 'plate of one of the condensersnecessary to equalize the capacities of the condensers is madel if thedetector is of the type, inwhich the outer chambers 19, 2li are cut offfrom one another, the adjustment in condenser capacity above described,nulliiies the effect of difrerlences in pressure of the gas masses onopposite sides of theV two membranes and differences -in the deiiectionof the two membranes resulting from 'differences in their thickness andtension. lf the detector is of the type, in

which the chambers 19, 20 are .connected by one or more connections 40,so that the gas masses in the two chambers act as one, the adjustment incondenser capacity nullifies the effect of differences in the deilectionof they membrances resulting from differences in their thickness andtension.

secure the' abutment member to the insulating ring 55.

A lead 73 is connected to one of the screws 72 and also to a terminalconnection 74 sealed through a body of glass 75 mounted in a sleeve 76,which is secured an opening through the wall of block 17 leading to thechamber containing the condenser. The bottom of the block 17 haschambers 77, into which the terminals 74 extend, and the chambers areconnected by a passage 78. A metalA rod 79 is mounted in insulatingbushings 80 in openings leading to chambers 77 and the rod extendsthrough the chambers and passage 78 and is connected to the outer endsof terminals 74. A lead 81 is attached to the rod and may extend to apreamplifier, in which While the capacity `changes in Athe condenser-,sare .converted into voltage changes, .as disclosed in the Vco-pendingapplicationpf Woodhull and T isdale, above identified.

'The electrical connection for the condensers are diagrammaticallyillustrated in Fig. 7. As there shown, the :two membranes 51 are, ineffect, connected to a line S2 and the `two fixed plates 6l of thecondensers .are connected ,to a line A83. The two condensers are thusconnected in parallel and lines 82, S3 may lead to the preampliiier ,84,mentioned above.

.I claim:

l. In a radiation detector, a gas-.tight housing, a pair of 4electricalcondensers within the housing, each condenser including a flexiblemembrane and a plate, the membranes lying with their planes parallel andsubdviding .the housing ,into a pair 4of Outer Chambers containing,respectiye .plates and a central chamber between the membranes, thethree chambers Containing a lling of same aas Yat the .Same pressure, aWindow in the wall of the housing and partly defining the centralchamber, r`the window Vadmitting radiation directly into the vcentralchamber, and a circuit, in which the condensers yare so connected thatthe combined capacity Vof the condensers varies in response to changesin gas pressure Within the central chamber but remains unchanged as themembranes move in unison in response to translational accelerationsacting on the housing.

2. kIn a radiation detector, a housing .containing a pair .of outerchambers and a central chamber between them, a .pair yof electricallyconductive membranes separating respective outer chambers from thecentral chamber and ,lying their planes parallel, the chambers allhaving a filling of the same gas at the same pressure and the centers ofgravity of the gas .masses in the three chambers lying yon a line normalto the .planes of the membranes with the center of gravity yof the gasmass in the central chamber equidistant from the centers of gravity ofthe gas masses inthe outer chambers, a plate mounted in opposition toeach membrane and forming an electrical vcondenser therewith, a windowin the wall ofthe housing and ,partly deiining the .central chamber, thewindow admitting radiation directly into the central chamber, anlelectrical connection between `the membranes, and an electricalconnection between the plates.

3. In a radiation detector, a housing containing a pair of outerchambers .and .a central chamber between them, a pair of electricallyconductiye 4membranes separating respective cuter members from ,theYCerf-fill Chamber and lying with their planes parallel, the chambersal1 having a lling of the same gas at the same pressure and the centersof gravity of the gas masses in the three chambers lying on a linenormal to the planes of the membranes with the center of gravity of thegas mass in the central chamber equidistant from the centers of gravityof the gas masses in the outer chambers, a plate in each outer chambermounted in opposition to the adjacent membrane and forming an electricalcondenser therewith, a window in the wall of the housing and partlydeiining the central chamber, the Window admitting radiation directlyinto the central chamber, an electrical connection between themembranes, and an electrical connection between the plates.

4. In a radiation detector, a housing -containing a pair of outerchambers and a central chamber between them, a pair of electricallyconductive membranes separating respective outer chambers from thecentral chamber and lying with their planes parallel, the chambers allhaving a lling of the same gas at the same pressure and the centers ofgravity of the gas masses in the three chambers lying on a line normalto the planes of the membranes with the center of gravity of the gasmass in the central chamber equidistant from the centers of gravity ofthe gas masses in the outer chambers, a plate mounted in opposition toeach membrane and forming an electrical condenser therewith, a windowfor admitting radiation directly into the central chamber and lyingnormal to the planes of the membranes, an electrical connection betweenthe membranes, and an .electrical connection between the plates.

5. In a radiation detector, a housing containinga pair of outer chambersand .a central chamber between them, a ,pair of electrically conductiveAmembranes separating respective outerchambers from the central chamberand lying with their planes parallel, the chambers all having a lling ofAthe same gas at the same pressure, a plate in each outer chambermounted in opposition to the adjacent membrane and forming an electricalcondenser therewith, a Window in the wall of the housing vand partlydefining the central chamber, the window admitting radiation directlyinto the central chamber, equalizing ducts connecting the centralchamber to the outer chambers kand maintaining equal gas temperaturesand pressures in the chambers through long period thermal changes, anelectrical connection between the plates, and an electrical connectionbetween the membranes.

6. In a radiation detector, a housing containing a pair of outerchambers and a central chamber between them, a pair of electricallyconductive membranes separating respective `outer chambers from thecentral chamber and lying with their planes parallel, the chambers allhaving a lling of the same gas at the same pressure, a plate in eachouter chamber mounted in opposition to the adjacent membrane and formingan electrical condenser therewith, a window in the wall of the housingand partly deiining the central chamber, the window admitting radiationdirectly into the central chamber, an electrical connection between theplates, an electrical connection between the' membranes, a passage.connected to the three chambers, and a valve for closing the passageand shutting off the chambers from one another.

7. In a Vradiation detector, a gas-tight housing, a pair of .electricalcondensers within the housing, each condenser including a iiexiblemembrance and a plate, the membranes lying with their planes paralleland subdividing the housing into a pair of outer chambers containingrespective .plates and a central chamber between Vthe membranes, .the.three chambers containing a lilling of the same gas at the samepressure, means for varying the spacing' of each plate from itsassociated membrane, a window lfor admitting radiation directly into thecentral chamber, and a circuit, in which the .condensers are soconnected that the Vcombined `capacity of the condensers varies in.response to changes in gas pressure within the central/.chamber :butremains unchanged as :the membranes move in unison in response totranslational accelerations acting on the housing.

S. In a radiation detector, a housing containing a pair of outerchambers and a central chamber between them, a pair of electricallyconductive membranes separating respective outer chambers from thecentral chamber and lying with their planes parallel, the chambers allhaving a filling of the same gas at the same pressure, a plate in ea-chouter chamber -mounted in opposition to the adjacent membrane andforming an electrical condenser therewith, an abutment engaging theouter face of each plate adjacent its periphery, means on the abutmentengaging the central portion of each plate and operable to vary thespacing between said central portion and its associated membrane, awindow for admitting radiation directly into the central chamber, anelectrical connection between the plates, and an electrical connectionbetween the membranes.

9. In a radiation detector, a housing having a central partitionsubdividing the housing into a pair of outer chambers and containing acentral chamber having openings leading to the respective outerchambers, a ilexible conductive membrane mounted in each outerchamberopposite the opening in the adjacent partition, a plate mountedin opposition to the membrane and forming an electrical condenser withthe membrane, a window mounted on the central partition for admittingradiation directly into the central chamber, an electrical connectionbetween the membranes, and an electrical connection between 'the plates.

10. In a radiation detector, a support formed of a pair of memberssecured together and deiining a space betweenl them, an annular abutmentattached to one of the members and lying within -the space, a metalplate mounted on the abutment within the space, the abutment engagingthe plate near its periphery, a exible conductive membrane having itsmargin clamped between the members and lying on the side of the plateremote from the abutment, the membrane and plate forming an electricalcondenser, and cooperating means on the abutment and plate forv varyingthe spacing between the portion of the plate within the abutment and themembrane.

11. In a radiation detector, a flexible electrically conductivemembrane, means for clamping a zone of the membrane, a conductive platelying face to face with and spaced from theY membrane, an abutmentengaging a zone of the outer face of the plate, and means for exing thearea of the plate inward from the abutment to vary the spacing betweensaid area and the membrane.

l2. In a radiation detector, a flexible electrically conductivemembrane, means for clamping a zone of the membrane, a metal plate lyingface to face with and spaced from the membrane, an abutment engaging azone of the outer face of the plate, and means extending through theabutment and secured to the plate, said means being operable to ex thearea of the plate inward from the abutment to vary the spacing betweensaid area and the membrane.

13. In a radiation detector, a housing, a pair of spaced exibleelectrically conductive membranes mounted in the Ihousing with theirplanes parallel and subdividing the interior of the housing into a pairof outer chambers and a central chamber between them, a connectionbetween the outer chambers, the chambers al1 having a lling of the samegas at the same pressure and the center of gravity of the combined gasmasses in the two outer chambers coinciding with the center of gravityof the gas mass in the central chamber, a plate within each outerchamber cooperating with the adjacent membrane to form au electricalcondenser, and a window in the wall of the housing and partly definingthe central chamber, the window admitting radiation ydirectly into thecentral chamber.

14. In a radiation detector, a housing, a pair of spaced iieXibleelectrically conductive membranesy mounted in the housing with theirplanes parallel and subdividing the interior of the housing into a pairof outer chambers and a central chamber between them, a connectionbetween the outer chambers, the chambers all having a lling of the samegas at the same pressure and the center of gravity of the combined gasmasses in the two outer chambers coincidingV with the center of gravityof the gas mass in the central chamber, -a pair of conductive plateslying face to face with respective membranes and cooperating with themembranes to form electrical condensers, means for connecting themembranes together, means for connecting the plates together, and awindow in the wall of the housing and partly defining the centralchamber, the window admitting radiation directly into the centralchamber.

15. In a radiation detector, a housing, a pair of spaced flexibleelectrically conductive membranes mounted in the housing with theirplanes parallel and subdividing the interior of the housing into `a pairof outer chambers and a central chamber between them, means forconnecting the outer chambers, said means including continuously openpassages connected to respective chambers on opposite sides of the axesthereof, the chambers all having a lling of the same gas at the samepressure'and the center of gravity of the combined gas masses in the twoouter chambers :coinciding with the center of gravity of the gas mass inthe central chamber, a plate within each outer chamber cooperating withthe adjacent membrane to form an electrical condenser, and a window inthe wall of the housing and partly dening the central chamber, thewindow admitting radiation directly into the central chamber.

16. A radiation detector in accordance with claim 11 wherein said meansfor flexing an area of said plate comprises coarse and ne degrees ofadjustment.

17. A radiation detector in accordance with claim ll wherein said meansfor flexing an area of said plate comprises co-axial screws of diierentpitch arranged to adjustably displace said area.

18. A radiation detector in accordance with claim l1 wherein the area ofsaid plate which is flexed inward is substantially less than the wholeof said conductive plate.

References Cited in the file of this patent UNITED STATES PATENTS2,424,976 Golay et al. Aug. 5, 1947 2,648,775 Waters Aug. 11, 1953V2,681,415 Liston June 15, 1954

